EDM crack removal tooling

ABSTRACT

A tool system features an EDM crack removal head which can be positioned within a nozzle/thermal sleeve and then oscillated in a vertical and horizontal directions to enable precise material removal, leaving the surface free of cracks and in a condition for rewelding if required. If a crack is found in a surface which is covered by a thermal sleeve, then a small specialized EDM cutting head, which can be delivered from the under side of the reactor head and has an ability to pass through the ID of the thermal sleeve, is used. The head enables the sleeve to be cut and allow a portion of the sleeve to be removed. The crack can then be removed using a crack removal type of head.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a crack removal tool. Morespecifically, this invention relates to a crack removal tool whichutilize EDM techniques and which are suitable for removing cracks whichappear within conduits, nozzles and the like, such as are found innuclear reactor related structures.

2. Description of the Related Art

During inspection of certain types of nozzle penetrations in pressurizedwater nuclear reactor heads, cracks may be discovered in weld areas ofone or more nozzles. Access to these defects is severely hindered by thepresence of thermal sleeves which are welded in place in nozzles andwhich prevent access with tooling. Accordingly, it is extremelydifficult to effect repairs.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide cutting and removaltools or heads which simplify the removal and repair of cracks whichtend to develop in nozzle penetrations and similar types of conduitingwhich are used in nuclear reactors and the like type of environments.

In brief, the above object is achieved through the use of EDM (electrodischarge machining) heads which were developed so as to permit thecutting and partial removal of a thermal sleeve so as to expose acracked area to permit defect blending within the head penetration

In brief, the above object is achieved through the use of a tool systemwhich features an EDM crack removal head which can be positioned withinthe nozzle or thermal sleeve and then oscillated in vertical andhorizontal directions to enable precise material removal, leaving asurface free from cracks and in a condition for rewelding if required.

In the event that a crack is found in a surface which is covered by athermal sleeve, a small specialized EDM cutting head which can bedelivered from an under side of the reactor head, and which has theability to pass through the ID of the thermal sleeve, is used to cut thethermal sleeve and allow a portion of the sleeve to be removed. Thecrack can then be readily removed using the crack removal type of head.

The use of the tooling system according the present invention enablesrepair of cracked nozzles in PWR heads from the underside, thuseliminating a costly need to remove a control rod drive mechanism andassociated hardware from a reactor.

More specifically, a first aspect of the present invention resides in atool for use with conduiting, comprising: an elongated shaft structure;first and second support members disposed on the shaft structure whichengage an inner wall of a conduit when actuated; cutting head means,supported on the shaft structure between the first and second supportmembers, for performing a cutting operation on an inner wall of theconduit, the cutting head means including a movable cutting electrodeand first servo means for selectively moving the electrode memberlaterally outwardly with respect the shaft structure; and second servomeans, operatively connected with the cutting head mean for selectivelydisplacing the cutting electrode in at least one of first and secondrotational directions.

A second aspect of the present invention resides in a crack removal toolcomprising: an elongate shaft structure; first and second inflatablemembers disposed on the shaft structure; a crack sensor supported on theshaft structure at a location between the first and second inflatablemembers; a crack removal head supported on the shaft between the firstand second inflatable members at a predetermined distance from the cracksensor, the crack removal head including a removal electrode andelectrode servo means for selectively displacing the removal electroderadially with respect to an axis of the shaft structure; and head servomeans for selectively displacing the crack sensor and the crack removalhead with respect to the first and second inflatable members and forcausing the crack removal head to undergo rotation about the axis of theshaft structure in at least one of first and second rotationaldirections.

A third aspect of the present invention resides in a sleeve cutting toolcomprising: an elongate shaft structure; first and second inflatablemembers disposed on the shaft structure; a cutting head supported on theshaft between the first and second inflatable members, the cutting headincluding a cutting electrode and cutting electrode servo means forselectively displacing the cutting electrode radially with respect to anaxis of the shaft structure; and cutting head servo means forselectively displacing the cutting head in at least one of first andsecond rotational directions.

A fourth aspect of the present invention resides in a crack removalsystem comprising: a crack removal tool which comprises: a firstelongated shaft structure; first and second selectively actuatablesupport members disposed on the shaft structure; a crack sensorsupported on the shaft structure at a location between the first andsecond support members; a crack removal head supported on the shaftbetween the first and second support members at a predetermined distancefrom the crack sensor, the crack removal head including a crack removalelectrode and a first servo means for selectively displacing the crackremoval electrode radially with respect to an axis of the shaftstructure; and second servo means for selectively axially displacing thecrack sensor and the crack removal head with respect to one of the firstand second support members and for causing the crack removal head toundergo rotation about the axis of the shaft structure in at least oneof first and second rotational directions.

A fifth aspect of the present invention resides in a crack removalsystem further comprising: a sleeve cutting tool which comprises: asecond elongate shaft structure; third and fourth selectively actuatablesupport members disposed on the second shaft structure; a cutting headsupported on the shaft between the third and fourth support members, thecutting head including a cutting electrode and third servo means forselectively displacing the cutting electrode radially outwardly withrespect to an axis of the second shaft structure; and fourth servo meansfor selectively causing the cutting head to undergo rotation about theaxis of the shaft structure in at least one of first and secondrotational directions.

A further aspect of the present invention is presented in a method ofrepairing cracks in a nozzle in which a sleeve is fixedly disposed,comprising the steps of: inserting sleeve cutting tool into the sleeve;activating support means which engages the inner wall of the sleeve andwhich maintains the sleeve cutting tool in a predetermined positionwithin the sleeve; cutting through the sleeve using the sleeve cuttingtool in a manner which allows a portion of the sleeve to be removed;removing the portion of the sleeve; inserting a crack removing tool intothe portion of the nozzle wherein the sleeve has been removed;activating support means on the crack removing tool to support the crackremoving tool in the nozzle; using a crack detecting sensor to locatethe position of a crack in the nozzle; moving the crack detecting sensoraway from the location at which the crack is detected and moving a crackremoval head into position opposite the location whereat the crack wasdetected; and removing portion of the inner wall of the nozzle using thecrack removal head.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more clearly appreciated as adiscussion of the preferred embodiments proceeds with reference to theappended drawings in which:

FIGS. 1 and 2 are schematic sectional views showing a sleeve cuttingtool and a crack removal tool in operative positions, respectively;

FIG. 3 is a plan view showing a sleeve cutting electrode which is usedwith the cutting tool shown in FIG. 1;

FIG. 4 is a plan view showing a removal electrode which is used with thecrack removal tool of the nature shown in FIG. 2

FIGS. 5 and 6 ar side elevations showing variants in the crack removalelectrode configurations;

FIG. 7 and 8 are side sectional elevations showing details of apreferred embodiment of a sleeve cutting tool according to the presentinvention;

FIGS. 9 and 10 are side sectional elevations which show the crackremoval tool with the crack removal electrode in raised and loweredpositions respectively;

FIG. 11 is a front sectional elevation showing the crack removalelectrode in its lowered position; and

FIG. 12 is a side sectional elevation showing the mechanism via whichthe crack removal electrode is reciprocated and oscillated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic side sectional elevation showing a sleeve cuttingtool 1 according to the present invention. This tool basically comprisestwo concentrically arranged shafts 2, 4 which are reciprocal withrespect to one another. Both shafts 2, 4 are hollow. The outer shaft 2supports the inner shaft 4 concentrically therein and in a manner whichallows the inner shaft to rotate relative thereto.

Selectively inflatable upper and lower bladder assemblies 6, 8 aresupported on the shaft assembly. These bladder assemblies 6, 8 areconnected with a source of pneumatic or hydraulic pressure via conduits.Note that only the conduit 7 which supplies the upper bladder assemblywhich extends all the way up the hollow inner shaft and which isillustrated as extending out of the top of the inner shaft 4 and curvingback down to the upper bladder assembly 6, is shown.

An EDM cutting head 10 is supported between the upper and lower bladderassemblies 6, 8. The cutting head 10 is in a drive connection with theinner shaft so as to be synchronously rotatable therewith. In theembodiments of the invention, the inner shaft 4 is connected with ahydraulic motor 12 which can drive the shaft in either rotationaldirection. The motor 12 is controlled by a switching control (not shown)which reverses the direction the motor is driving the shaft each 360° to370° rotation (for example). While it is possible to continuously drivethe shaft 4 only in one rotational direction, it is preferred to inducethe above type of oscillation in that it simplifies the electricalconnection between the base 11 and the EDM cutting head. For example,the oscillation eliminates the need for brushes and the like to maintainconstant electrical communication between the base of the cutting tooland the cutting head.

The cutting head 10 includes a hydraulically operated motor 13 (see FIG.7, for example) which allows the cutting electrode 14 to be displacedwith respect to the axis of rotation of the inner shaft 4 and thusallows the eccentricity of the cutting electrode 14 to be varied.

In the situation illustrated in FIG. 1, it is assumed that a crack hasbeen detected in a portion of the nozzle 16 which is covered with athermal sleeve 18. In accordance with this detection, the cutting tool 1is inserted into the thermal sleeve 18 so that the cutting electrode 14is located at a level which is between the crack and the site where thethermal sleeve 18 is welded to the nozzle. The upper and lower bladderassemblies 6,8 are inflated so that the tool 1 is retained in place andthe cutting tool is temporarily secured in place. The EDB cuttingprocess is then initiated. In FIG. 1, the cutting electrode 14 has beengradually displaced laterally until such time as the EDM cutting actionhas cut almost through the thermal sleeve 18 which is fitted within thenozzle.

After the thermal sleeve 18 is cut all the way through, the cuttingelectrode 14 is retracted to a position of minimal projection, the upperand lower bladder assemblies 6, 8 are deflated and the sleeve cuttingtool is removed. Following this, the free end portion of the thermalsleeve 18 is pulled from the nozzle 14, thus exposing the portion of the16 nozzle in which the crack is formed.

Following the removal of the thermal sleeve, the crack removal tool 20is inserted into the nozzle 16.

As shown in FIG. 2 the crack removal tool 20 basically comprises upperand lower bladder assemblies 22, 24 which are larger than those providedon the sleeve cutting tool. In this arrangement the lower bladderassembly 24 is supported on the outer shaft 26 while the upper bladderassembly 22 is slidably disposed on the inner shaft 28. The cutting head(hereinafter referred to as the crack removal head) 30 and a crackdetection sensor 32 are mounted on the inner shaft so as to bedisplaceable relative to the lower bladder assembly 24. Although notclear from this figure, the inner shaft 28 is arranged to bedisplaceable through a relatively large distance with respect to theouter shaft (see FIG. 12 for example). The reason for this is that, whenthe crack removing tool 20 is inserted into the nozzle 16, it isimpossible to see the crack or to determine when it has been removed.Accordingly, the crack detector 32 is provided. In this instance, thedetector is an eddy current type detection.

The crack detector 32 is energized and moved both axially androtationally, until such time as the crack or flaw is located. After theposition of the crack is identified, the inner shaft 28 is displaced(upwardly as seen in the drawings) through a predetermined distancewhich locates the crack removal electrode 34 immediately opposite thecrack. EDM cutting is then initiated and the metal around the crack isremoved. Since the amount of metal which is being removed cannot bemeasured while the tool is in position, the metal removal is continuedfor a predetermined time. This time is determined by empirical data fromwhich it is able to relatively accurately estimate how much metal isremoved per unit time.

After the predetermined time (for example, 1 hour) the EDM cutting isstopped and the inner shaft 28 retracted to return the crack sensor 32to the crack site. If the crack is still detected, the EDM cuttingelectrode 34 is moved back into position and metal is removed foranother predetermined period of time. These cutting/checking steps arerepeated until such time as the crack is no longer detected.

However, since the accuracy of the crack detector 32 is limited, afterthe crack is detected as having been eliminated, the metal removalprocedure is repeated once more but for a shorter period of time (e.g.40 mins) to ensure total removal.

When this last metal removal process is completed, the bladderassemblies 22, 24 are deflated and the tool 20 is extracted from thenozzle.

Depending on the amount of metal which has been removed, it may benecessary to fill the newly created void with a suitable weld materialor the like. If desired, the crack removal tool can be reinserted andthe surface of the weld material smoothed via EDM cutting to exactly therequired ID.

The cut-off portion of the thermal sleeve 18 can be reinserted andbutt-welded to the portion still fixed within the nozzle, thuscompleting the repair.

It will be noted that in addition to the 360° to 370° oscillation, it ispossible to reciprocally move the metal removal electrode 34 up and downwhile the rotational motion is taking place to remove long cracks. It isalso possible to use different shaped metal removal electrodes of thenature depicted in FIGS. 5 and 6, for example. The type (for example,shape) can be selected based on the width and length of the crack thatneeds be removed.

As will be appreciated by those skilled in the art of EDM, it isnecessary to continuously supply a flow of dielectric fluid between theinterface defined between the electrode and the surface of work piecebeing cut. This fluid, along with pressurized fluid(s) which controlsthe operation of the hydraulic motor 36 used to determine the lateraldisplacement of the crank removal electrode 14, is supplied via conduitswhich are passed upwardly through the interior of the hollow inner shaft28. It will be understood that a similar conduiting arrangement isprovided in the sleeve cutting tool 1.

In the case of the crack removal tool, two motors 40, 42 are required atthe base. One motion 40 is for inducing rotational motion and the othermotion 42 is for producing reciprocal or axial motion 42.

The control of the hydraulic motors 12, 13, 36, 40, 42 of the cuttingand removal tools 1, 20 is controlled by controllers (no numerals) whichare operatively connected with the tools in the representative mannershown in FIGS. 1 and 2.

In this instance, de-ionized water is used as the dielectric fluid andis constantly circulated through the space defined between theinflatable bladder assemblies. In the case of the crack removalelectrodes shown in FIGS. 5 and 6, through bores 38 are formed thereinin a manner which allows the dielectric fluid to be supplied to thecutting site.

It is worth noting at this point that the motors which are used toprovide rotational and reciprocal motion are preferably hydraulic orpneumatically operated types as differentiated from electricallyoperated motors. The reason for this is that even though the lowerinflatable bladders provide a reasonable seal with the inner surfaces ofthe thermal sleeve or nozzle, still some leakage occurs and the need tohermetically seal the motors and the like is avoided.

In order to establish a satisfactory electrical connection necessary forperforming EDM, it is possible to provide a leaf spring like contacts atthe upper ends of the tools, preferably at a location above the upperbladder assemblies.

The electrodes used in the above types of sleeve cutting and crackremoval tools can be made of materials such as copper-tungsten, tungstenand graphite. In the case of the thin sharp edged sleeve cuttingelectrode, the former two materials can be used. In the case of thecrack removal electrodes, the latter two types of material can findapplication.

It is of course within the scope of the invention that a number ofdifferent materials or composites can be used and a such the inventionis not specifically limited to the same.

FIG. 3 shows an example of the shape (as seen in plan) of the thincutting electrode used in the sleeve cutting tool.

FIGS. 7 and 8 show upper and lower portions respectively of a preferredembodiment of the sleeve cutting tool according to the presentinvention. In this figure, elements designated in FIG. 1 are designatedby like numerals.

FIGS. 9 to 12 show details of the crack removal tool according to apreferred embodiment of the device. FIGS. 9 and 10 show the crackremoval head in its upper and lower positions. As the upper bladdermember is slideably supported on the inner shaft, it is preferred tomove the crack removal head to its uppermost position at the time ofinsertion and to inflate the upper bladder. The crack removal head isthen lowered to its lowermost position and the lower bladder is theninflated. This separates the upper and lower bladders and improves thealignment of the tool within the nozzle.

It should also be noted that it is within the scope of the invention toreduce the diameters of the crack removal device and adapt the same foruse a thermal sleeve should a crack be discovered in a portion which isnot readily removed through the use of the sleeve cutting tool.

WHAT IS CLAIMED IS:
 1. A tool for use with conduiting, comprising:anelongate shaft structure; first and second support members disposed onsaid shaft structure, said first and second support members engaging theinner wall of a conduit when actuated; cutting head means, supported onsaid shaft between said first and second support members, for performinga cutting operation on the inner wall of the conduit, said cutting headmeans including movable cutting electrode and first servo means forselectively moving said electrode member laterally outwardly withrespect said shaft structure; and second servo means, operativelyconnected with said cutting head means for selectively displacing saidcutting electrode in at least one of first and second rotationaldirections.
 2. A crack removal tool comprising:an elongate shaftstructure; first and second inflatable members disposed on said shaftstructure; a crack sensor supported on said shaft structure at alocation between said first and second inflatable members; a crackremoval head supported on said shaft between said first and secondinflatable members at a predetermined distance from said crack sensor,said crack removal head including a removal electrode and electrodeservo means for selectively displacing said removal electrode radiallywith respect to an axis of said shaft structure; and head servo meansfor selectively displacing said crack sensor and said crack removal headwith respect said first and second inflatable members and for causingthe crack removal head to undergo rotation about the axis of said shaftstructure in at least one of first and second rotational directions. 3.A sleeve cutting tool comprising:an elongate shaft structure; first andsecond inflatable members disposed on said shaft structure; a cuttinghead supported on said shaft between said first and second inflatablemembers, said cutting head including a cutting electrode and cuttingelectrode servo means for selectively displacing said cutting electroderadially with respect to an axis of said shaft structure; and cuttinghead servo means for selectively displacing said cutting head in atleast one of first and second rotational directions.
 4. A crack removalsystem comprising:a crack removal tool which comprises:a first elongateshaft structure; first and second selectively actuatable support membersdisposed on said shaft structure; a crack sensor supported on said shaftstructure at a location between said first and second support members; acrack removal head supported on said shaft between said first and secondsupport members at a predetermined distance from said crack sensor, saidcrack removal head including a crack removal electrode and a first servomeans for selectively displacing said crack removal electrode radiallywith respect to an axis of said shaft structure; and second servo meansfor selectively axially displacing said crack sensor and said crackremoval head with respect one of said first and second support membersand for causing the crack removal head to undergo rotation about theaxis of said shaft structure in at least one of first and secondrotational directions.
 5. A crack removal system as set forth in claim 4further comprising:a sleeve cutting tool which comprises: a secondelongate shaft structure; third and fourth selectively actuatablesupport members disposed on said second shaft structure; a cutting headsupported on said shaft between said third and fourth support members,said cutting head including a cutting electrode and third servo meansfor selectively displacing said cutting electrode radially outward withrespect to an axis of said second shaft structure; and fourth servomeans for selectively causing said cutting head to undergo rotationabout the axis of said shaft structure in at least one of first andsecond rotational directions.
 6. A tool as set forth in claim 1, whereinsaid first and second support members comprise inflatable bladders.
 7. Atool as set forth in claim 1, as set forth in claim 1, wherein saidfirst and second support members are displaceable relative to oneanother in accordance with the axial displacement of said crack detectorand said crack removal head.